On the Joint Security of Encryption and Signature, Revisited

Abstract

Abstract. We revisit the topic of joint security for combined public key schemes, wherein a single keypair is used for both encryption and signature primitives in a secure manner. While breaking the principle of key separation, such schemes have attractive properties and are sometimes used in practice. We give a general construction for a combined public key scheme having joint security that uses IBE as a component and that works in the standard model. We provide a more efficient direct construction, also in the standard model. We then consider the problem of how to build signcryption schemes from jointly secure combined public key schemes. We provide a construction that uses any such scheme to produce a triple of schemes – signature, encryption, and signcryption – that are jointly secure in an appropriate and strong security model.